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Father’s genes can delay baby’s birth

A father’s genes can increase the risk of a lengthy pregnancy by 30 per cent, new research shows. The discovery was made by Danish researchers analysing late births in pregnant women.

They found that women who had an unusually long first pregnancy, were less significantly less likely to have a second long pregnancy if the second baby had a different father.

This shows, says Annette Wind Olesen at the University of Aarhus, that a father’s genes partly determine the timing of his child’s birth. “It was very exciting to find out that there was a difference between fathers,” she says. “Knowledge about the birth mechanism is very sparse.”

The team is the first to investigate the role of the father in long pregnancies, which they defined as longer than 42 weeks. They considered environmental factors, such as social status and area of residence, but found no effect. They also note that artificial induction of labour is rare in Denmark before 42 weeks.

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Five per cent of all births are delayed. And a long pregnancy brings greater risks of complications for both mother and child.

Different dads

Olesen and her colleagues looked at 22,000 women who had a late first pregnancy and then went on to have another child between 1980 to 1994. They selected 7000 women from all women mothers of two or more children as controls.

The risk of having a second late baby was 19.9 per cent, they found. In contrast, women whose first pregnancy was in the standard 37 to 41 week range had only a 7.7 per cent risk of the second pregnancy being unduly long.

However, if women who had experienced a prolonged first pregnancy changed partner, their risk of having a second prolonged pregnancy fell to 15.4 per cent. “If you changed the father the risk of this recurring was reduced by 30 per cent,” Olesen told New Scientist.

The next step for the research could be to determine which genes can induce a delay or whether there are any evolutionary advantages conferred by a paternal ability to influence the length of a pregnancy. One possibility might be that longer pregnancies produce babies that are more likely to survive after birth, though this would be balanced by the increased risk posed to the mother of delivering a larger baby.